.\"-
.\" Copyright (c) 2002-2003 Networks Associates Technology, Inc.
.\" Copyright (c) 2004-2017 Dag-Erling Smørgrav
.\" All rights reserved.
.\"
.\" This software was developed for the FreeBSD Project by ThinkSec AS and
.\" Network Associates Laboratories, the Security Research Division of
.\" Network Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035
.\" ("CBOSS"), as part of the DARPA CHATS research program.
.\"
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.Dd May 31, 2025
.Dt PAM_CONV 3
.Os
.Sh NAME
.Nm pam_conv
.Nd PAM conversation system
.Sh LIBRARY
.Lb libpam
.Sh SYNOPSIS
.In security/pam_appl.h
.Bd -literal
struct pam_message {
	int      msg_style;
	char    *msg;
};

struct pam_response {
	char    *resp;
	int      resp_retcode;
};

struct pam_conv {
	int     (*conv)(int, const struct pam_message **,
	    struct pam_response **, void *);
	void    *appdata_ptr;
};
.Ed
.Sh DESCRIPTION
The PAM library uses an application-defined callback to communicate
with the user.
This callback is specified by the
.Vt struct pam_conv
passed to
.Fn pam_start
at the start of the transaction.
It is also possible to set or change the conversation function at any
point during a PAM transaction by changing the value of the
.Dv PAM_CONV
item.
.Pp
The conversation function's first argument specifies the number of
messages (up to
.Dv PAM_MAX_NUM_MSG )
to process.
The second argument is a pointer to an array of pointers to
.Vt pam_message
structures containing the actual messages.
.Pp
Each message can have one of four types, specified by the
.Va msg_style
member of
.Vt struct pam_message :
.Bl -tag -width 18n
.It Dv PAM_PROMPT_ECHO_OFF
Display a prompt and accept the user's response without echoing it to
the terminal.
This is commonly used for passwords.
.It Dv PAM_PROMPT_ECHO_ON
Display a prompt and accept the user's response, echoing it to the
terminal.
This is commonly used for login names and one-time passphrases.
.It Dv PAM_ERROR_MSG
Display an error message.
.It Dv PAM_TEXT_INFO
Display an informational message.
.El
.Pp
In each case, the prompt or message to display is pointed to by the
.Va msg
member of
.Vt struct pam_message .
It can be up to
.Dv PAM_MAX_MSG_SIZE
characters long, including the terminating NUL.
.Pp
On success, the conversation function should allocate and fill a
contiguous array of
.Vt struct pam_response ,
one for each message that was passed in.
A pointer to the user's response to each message (or
.Dv NULL
in the case of informational or error messages) should be stored in
the
.Va resp
member of the corresponding
.Vt struct pam_response .
Each response can be up to
.Dv PAM_MAX_RESP_SIZE
characters long, including the terminating NUL.
.Pp
The
.Va resp_retcode
member of
.Vt struct pam_response
is unused and should be set to zero.
.Pp
The conversation function should store a pointer to this array in the
location pointed to by its third argument.
It is the caller's responsibility to release both this array and the
responses themselves, using
.Xr free 3 .
It is the conversation function's responsibility to ensure that it is
legal to do so.
.Pp
The
.Va appdata_ptr
member of
.Vt struct pam_conv
is passed unmodified to the conversation function as its fourth and
final argument.
.Pp
On failure, the conversation function should release any resources it
has allocated, and return one of the predefined PAM error codes.
.Sh RETURN VALUES
The conversation function should return one of the following values:
.Bl -tag -width 18n
.It Bq Er PAM_BUF_ERR
Memory buffer error.
.It Bq Er PAM_CONV_ERR
Conversation failure.
.It Bq Er PAM_SUCCESS
Success.
.It Bq Er PAM_SYSTEM_ERR
System error.
.El
.Sh SEE ALSO
.Xr openpam_nullconv 3 ,
.Xr openpam_ttyconv 3 ,
.Xr pam 3 ,
.Xr pam_error 3 ,
.Xr pam_get_item 3 ,
.Xr pam_info 3 ,
.Xr pam_prompt 3 ,
.Xr pam_set_item 3 ,
.Xr pam_start 3
.Sh STANDARDS
.Rs
.%T "X/Open Single Sign-On Service (XSSO) - Pluggable Authentication Modules"
.%D "June 1997"
.Re
.Sh AUTHORS
The OpenPAM library and this manual page were developed for the
FreeBSD Project by ThinkSec AS and Network Associates Laboratories,
the Security Research Division of Network Associates, Inc.\& under
DARPA/SPAWAR contract N66001-01-C-8035
.Pq Dq CBOSS ,
as part of the DARPA CHATS research program.
.Pp
The OpenPAM library is maintained by
.An Dag-Erling Sm\(/orgrav Aq Mt des@des.dev .
